1. Field of the Invention
The present invention relates to a welding control system in an automatic welding machine, and more particularly to a welding control system in an automatic welding machine, which can obtain a weaving pattern suitable for a workpiece to be welded.
2. Description of the Related Art
Arc welding machines operate by applying a voltage between a wire and a workpiece to be welded to produce an arc from the distal end of the wire, causing the wire and the workpiece to be melted at a low rate by the heat generated by the arc, and moving the distal end of the wire along a welding path while feeding out the wire continuously at a slow rate, for thereby welding the workpiece. FIG. 6 of the accompanying drawings schematically shows such an arc welding machine. In FIG. 6, a wire WR is fed by rollers FR in small increments in the direction of the arrow, and passes through a guide member GB to project from the distal end of a torch TC. The rate of feed of the wire WR is limited such that the distal end of the wire will be spaced a prescribed distance from the surface of a workpiece WK to be welded. The positive potential of a high voltage which is generated by a welding power supply PS is applied to the wire WR through the guide member GB, whereas the negative potential is connected to the workpiece WK. A gas is supplied from a gas supply (not shown) in the direction of the arrows through the torch TC and applied to the workpiece WK to prevent a welded area from being oxidized. When the gas is supplied from the gas supply and the high voltage is generated by the welding power supply PS while the wire is fed out in small increments, an arc is produced from the distal end of the wire, and the wire and the workpiece are melted such that the melted portion is integrally welded. Such a welding operation is performed by a robot. More specifically, the torch of the welding machine is gripped by the robot, and the torch (distal end of the wire) is moved by the robot along a welding path to weld the desired portion. In order to enable the robot to weld the workpiece, it is necessary to teach the robot the path or positions to which the torch is to be moved and the speed at which the torch is to be moved.
For welding the workpiece according to the taught positional data, it is the recent practice to provide a soft weaving ability achieved by composite motion produced by movements about 6 axes of the robot, i.e., a turn axis, an upper arm axis, a lower arm axis, and wrist axes.
FIG. 7 is a diagram showing, by way of example, a weaving pattern of soft weaving accomplished by the robot. For performing such weaving movement, a weaving command format in the program is indicated as EQU (G81, 1, f, a)
where G81 indicates a weaving command, 1 a number for denoting the weaving pattern (the pattern shown in FIG. 7), f a weaving frequency, and a a weaving amplitude. The weaving movement is limited to the pattern shown in FIG. 7 in which the weaving amplitude a remains the same on both sides of a central welding line CT. With this weaving movement, therefore, a welding material M is applied only uniformly on both sides of the central welding line of the workpiece WK as shown in FIGS. 8 and 9.
With more demands for complex motions of robots, a welding robot may be required to effect such a weaving movement as to cause a welding material to be applied in a manner to be diplaced to one side with respect to the central welding line. Although there are various reasons for such a weaving movement, typical examples are that when different metals are to be welded, or due to the shape of an area to be welded, the welding material may be displaced to one side to weld the workpiece more firmly on such one side.
However, the above weaving movement cannot heretofore been performed by welding robots.